Electrical measuring instrument



Dec. 8, 1931. E. L. MABIE 1,835,658

ELECTRICAL MEASURING INSTRUMENT Filed Aug. 2, 1930 2 Sheets-Sheet 1 Dec. 8, 19.31. E. 1.. \MABIE ELECTRICAL MEASURING INSTRUMENT Filed Aug. 2, 1930 2 Sheets-Sheet 2 EDMUND LI'MABIE, os -emeheo;

Patented Dec. 8 v1931 v .,2'"

IL INOIS, Ass- 101 011 JEWELLQELEGTRECALITNSERUMENT@ORPORATIQN, AIeoe-PeRArm re New JERSEY C R L iees ifie i ww i l The present inventionrelatesto electrical measuring instruments and 1s partlcularly concernedwith instruments ofthe type hav--- ing 1 a single spriii-g; or instruments hav.' ing axplura'lity of spri1'1 's,'soh 1e {*of Which are notaccessible-for acljustment."

In instruments ofthisftype it is -llighly desirable "tha tl16$13-l"l11g which is accessible for" adj hstmen't'vbe"providedlwith an adj ust= able spring abutmentwhich may beldeatecl' in any" of a 'pluralityfof adjustable positions so that the'torsionalstrength of thespring' and the {range of movement m be readily "ez'lto keept he poi ter'Withinthe range 01 e sealcatfull load and-to -bringtheini 'ti al position oi lthe' pointer nearlthe zero mark WlllCll ltlnaybe accuratelyadjusted by aadjustmentscrew if desiredfi V $11 the aJ hstine-nt or calibration of the elec trical instrumented the claissidescribed; it is cleslrablefiioas in'ble theIpaifts of the instru-- ment in "operative relation including the ing's which resist '1 the -(le fleet-io11' of the .Jointor; anrlinst tiical Values, such cr r 'a's-,*for instance, full load ent. 3 s e :f rt'should be uhderstooclthat the relative arc-portions of thejp'arts of the: instrument; the ofthe scaleancl scale d1 1s1ons,;s1zei and character" of springs aiid'fcoils, have be n predetermined loyfthe: construction and bration of a master 111strument,-and--all ly accorclingto pattern. may be found; however, a H r-"the first assembly of :any instrunie t s the deflection for full loadburrentfis slightly. reater erless' than the length 'of'the scale,

7 one to iiiiar'iichs in the physical' characteristics f thc parts, suchas the 'springs or other parts, and consequentlyitfisclesirable to ad ust 'tlielensionef one of the springs-whichresistkleflectionofthe pointerl":

1 21 increase in the efieetive length' of a ff 'given eross seetioh and material 5 increases the flexibility ofthe Whole,

the peiiiteryancl acleer ease 'ih Ltheefiective meats are' usually test ed;' to-observe the deflection at determined elec'-" the inst-l ment parts, incluitliiigg the sca-le and springs are thereafter made'substantlalen the 'instruineht is tested; that and consequently increases the deflection of.

leligth of the spring decreases the flexibility, Iacrea-"es' the relat ve strfinessand resistance to deflection-5 anal decreases tull 'load-"defieetion Whichis usually taken-ash standard al t ugh'any predeterminedstandard may-be 65 I le' assembl cf the i-nstrun'1ent; the a d sprmg may be permanently secured he m0v111g elemeht,but 1t is preferably se BY mesfiishssmmmmris, mo-

cared .te an adjustable 'spring abutment car aa-fl'fi; 1

meal

H e 'such mannerthat' 'the spring e releasecl and made loh er 01 shoreer,asfornsta be; the spring may: esecurerl by a drep of solder betweenthe 's' fn'ing and ahiltiriehtlfat jali aointwhich is sfiac ed froih wheeze! seam spring.-

1 r V I j That poi tion of the-enelofthe sp I g' ectiiig-bey0iiclv solder or other seeiil ing means'is merelyexcess-lengthierthe urpose i of rmittihg ah adjiistmentefthe length otthe spr-ingcand such exeess length oat-spring does-hot materiall y afi'e'c' instrument. Y

def iectiolrofthe I r The" instrument tllell "te'sted alid if the:

deflection is found to conform to-sta 1idard the excess length'of'springmay be clipped ofL-hut if the spring is too stiff as shown by a' scale 'clefieetio11' of less than the full scale at full load; the spring maybe loosened-from the abutment bytlreepplication of heat,- amt its efiective' lehgthii'ncreasecl securing the spring wthe 'abutmeiit again a-ta 'pointneare er "theendof thespr-ing; or if tl'l -ff-lill loail deflection is greater than-the scale; he spring may be shortened "until full loaddflectionooh-forhis-to' 'thescale} 1 I The scale being with respect to the. other parts "(if the-instrument When'these-ad j ustme hts have fbe'en maileg the no load cle-i fleetion "hot locate the pointer near zero;

spiral coil s ring rotates the anovi-n'g element which "is'satta cheelfte-the other" end of the spring; with respect tothescale, and it {is therefore necessary to provide an i adws't-a 'ble-abatmeht' ear the fixed end ofthe spring? having a agreatelv range o-f ad justment tham the usual zere correction screw 'WlIlCh isonly 1 adapted; 01 relatively small corrections. $1

In somecmbodiments ofethe invent-b rths 1 because the shortening or "le'n gthenin g 03E a 1 l entire range of adjustment may be provided by the adjustable spring abutment, and the zero correction screw may be eliminated so that anyzero adjustment or correction would be accomplished by removingthe cover and moving the adjustment spring abutment, but the higher grade instruments are preferably provided with a Zero correction screw or other device which is accessible from the outside of the instrument. 1 V

The spring adjustment devices of theprior art havenot been capable of adjustment over the complete range of rotation of three hundred sixty degrees, nor have the prior ade 'justment devices been capable of adjustment to rotate through. the full; range of adjustment of three hundred sixty degrees or more,

and whichis therefore more adaptable and flexible than the devices of the prior art.

7 Another object is the provision of approved adjustable spring abutment which is provided with positive securing. means such as a latching device for securing the abutment in any adjusted position, as distinguished from the mere frictional engagement between V the abutment and i the support or member to which it issecured Another object is the provision of a positively secured adjustable spring] abutment which may be released or secured without the necessity for special tools and the parts .of-

which lend themselves readily to manufacture by ordinary stamping operations, thereby reducing the cost of the instrument and bringing the instrument within the means of a larger number o'fpurchasers. 7

Another object is the provision of an improved electrical instrument assembly which iscapable of more economical manufacture than the devices of the prior art, and which is better adapted to withstand electrical and mechanical abuses. T v c v V Another-object is the provision of a simplifled electrical instrument having an improved spring abutment, an improved indieating unit, an improved casing, and'various other features and advantages which will be evident from the accompanying description and drawings in which similar characteristics and references indicate similar parts throughout the several views.

Referring to the drawings, of which there are two sheets,

Fig. 1 is a plan view of the front of an instrument constructed according to the present invention;

Fig. 2is an enlarged sectional view taken on the plane of the line 22 of Fig. 1;

Fig. 3 is a sectional view taken on the plane of the line 3 3'of Fig. 2;

- Fig. 4. is an enlarged sectional view taken on the plane of the line 4-4 of Fig. 2,

Fig. 5 is a view in perspective of the zero correction plate;

Fig. 6 is a plan view of the adjustable spring abutment plate.

, The instrument which has been selected to illustrate the invention is a volt meter of. the magnetic vane type, having a single spiral spring for resisting deflection of the pointer, but the features of the present invention may be embodied in volt meters, ammeters, or other instruments of the moving coil type or any other type employing a spring for which it is desirable to provide an adjustable spring abutment.

Referring to the drawings, the electrical instrument'lO is preferablyprovided with a casing 11 which may be formed by molding 'thesame of initially plastic material such as a phenolic condensation product or some other mold ng powder having electrical 1nsulating characteristics.

The casing 11 is preferably substantially cylindrical in form and provided with an open end 12 for exposing the dial 13 which is preferably protected by a transparent cover 14 of glass or other transparent material.

In order tosecure the glass cover in casing 11, the casing is preferably formed with an integral inwardly extending annular flange 15 at the opening12, and the glass 14 may be secured in placeby a bezel 16 comprising a metal ring-having an inwardly extending annular flange 17 and a substantially cylindrical body flange 18. The body flange 18 is adapted to be secured by frictional engagement with the interior cylindrical wall 19 of the casing 11, the glass being confined between the metal flange 17 of the bezel 16 and i the insulating flange 15 carried by the casing 11. a The glass is preferably provided with an aperture 20 within wliichis rotatably mounted a zero adjustment screw 21 adapted to be held in any adjusted position by the friction which is caused by spring washer 22 confined between the'glass and the rivet washer 23,

The washer 23 carries the usual eccentric pin 21 for engagement between the oppositely extending diagonal legs 25 of a zero corrector plate 26.

The casingll'may be provided with an integral annular attaching: flange 27 located adjacent the front of the instrument in the flush type of instrument, or the flange 27 gagef'the ;.sides-:of- Ithe coil 43 overt more than 31, and the'base 28 iniaysbe formed with :a'

reduced cylindrical portion? 32 iadaptedto fit in I the enlargement 30 and with a oylindrical part 33 adapted to engagethe inner w'all19.

of the casing l1. The base 28 may bese+- cured to the casingQZ-byhiplurality of screw bolts 34, extending.:througliathe wall ot'the casingill, and threaded into the'insulating material-of the base 28,.andthe screwloolts 34 are preferably uniformly spaced about 'the circuinfejrenceofthecasing11. V l

' The bottom 35 oil-the base 11 is substantially circular in form to correspondto the.

casing "11 and is preferablyprovided with a plurality of connectorjapertures 36 adapted to receive the connector bolts 37 which are provided ith-non ci-Tcular heads 38 adapted to be received in complementary non-circular socket 39-for1n'ed on the inside pf the bottom 35 for epreventingyrotation; of bolts 537.

Each of the bolts-237F1 3 preferabl-yv rovided with a spring was-her40and oneg-orinore nuts 41 for securing the bolt in theicasing, and for securing connectors to the outside'endsof bolts-37: V

; 3 Referring to Fig.3; the base 28 inafy be-provided witha plurality ofja-uxili'ary connector bolt sockets 42, for use in pr-oviding multiple connectors or taps on theins'tru nent coil 43," and the base may also be provided with a phi- V ralityso'ffinwardly projecting. bosses '44 for receiving and supporting. spools which carry multiplier coils or calibration resistancecoils when it is desirable toenibody the invention in instruments n which such co ls-are, neces:

sary or desirable. The lugs44 have threadedf apertures 45 U into which screw boltsi are threaded, the screw bolts passing through the spools. I

The base 28 is preferably-provided with the inwardly projecting annular wall 46 for engaging the inside of the casing; 11 :and the;

wall 46 maybe provided with an'inwardly projecting-boss 47 forxreceivingi-one of the, screw bolts 34. a

At the side of the base 28 where. theactuah ingcoil 43is located, thebase 28 is prefer: ably provided withan inwardlyvprojecting boss 48 which is formed with a socket 49 for receiving Y the actuating coil '43-. The size of the 'boss 48 'ispreterablyqsuchthat the socket 49inay extend about the coil 43 to the points 50; 51 which are substantially,- past "a diametrical in-e extending through.theaxis of the coi-lf43r soithatthe socket 49 isradapted teen secure it in its socket' 49; v

half its periphery, and the coil 43; isadapted to be slidablyxinserted: the socket'49. The boss; 48 preferably. aextends inward past the points 50; 51 .onea ch side of the coilto provide a support for a pair oicoilsecuriug platesi52', 53 which are preferably unounted in "complc nientary slots 54, 155respectively. i

' The *:coil securing +plates' 52, 53" cornprise elongated strips of resilient SllQGtHiQtfll', each stripbeing providedawithan aperture. 56 for receiving-theireduceclythreaded end 57 of a dial supporting postw58; The: engagement between the edges of the plates 52, 53 with tliew'alls 0f the complementary x-slotso-54, effectively prevents rnovernent of the coil securing plates52,=153 when they are secured inplace by'the threaded members 58 and the outer ends "59-of strips 52, 53 resiliently en'- gage the end ofi'the actuatingcoil 43 and A woven fabric boot-(id'suchxas a-"short length "of braided tubularrfabricliss-lidably mounted on boththe ends 59 of strips '52, 53 for preventingithe 'metal strips '52, 53 from damagingthe wire'ofia-ctuating coil 43*or shortr'circuitin g any of: the coils by wearing ofi'the in'sulationfih r A The boss 48 "is preferably; provided at each side witha'female inetafllicithreaded member 61 which i's embedded in'fthe insulating mater-iazl. of the-base 28; during the molding operationandadapted to receivethe threaded ends 57 of the dial supporting posts 58. In some embodiments of the invention the dial supporting post-s58 may be threa'ded directly into the insulating inat'eria-lsbut the imbedded v threaded-:rhembersi' 61' provide a more firm I and durable support for titer-dialsupporting posts 58. ::T he dial supporting: posts 58 com-' prise elongated metal nienibers' provided with reduced threaded portions 57 and formedwith aniiular shouldersz62 for engag cular wrench: engaging formations 63 and ingiand securing thestrips'525 53tl1eposts 58 being preferably provided withYnon-ci'r- A -11O with tl'ireaded bores 64 for receiving the stop screws 65. V

1- The' dial 13 comprises a -"substanti'allycircular plate of metal provided with an aperf ture' 67- surrouhding the bridgedS and pro'- vided' with a scale a 69 having l appropriate scale divisions" and 'indicia formed .on the surface of the insta l plate by etching, printing or bv pastingon layerof papero'n which the 1 scale and its indiciahave; been printed.:-- The dial 66 is providedzwith apair of -'apertures '70 for receiving the reduced threaded ends71 of the stop posts-65 and the dial :66? maybe secured in place bv the stop posts 65 which are" provided with. annular shoulders 72'and with an elongated bodyi7 3 adapted- *to be engaged by the needle 5 74' to limit excessive movement of the needle. zThe head 75 *of each stopfpostnis,-pi'eferablyuprovided-witha herf Z621 s' P insulating material having the elongatedoblong body 77 and a laterally projecting supporting and attaching flange 79 at one end.

The boss 48' on the base 28 is'pre'ferably providedwith a substantially flatupper sur-' face 80 in which are secured a plurality of female threaded metallic members 81,'these members being embedded'in the molding operation and adapted to engage the complementary threaded ends of screw bolts 82. Screw bolts 82 pass through apertures 83a in the supporting flange 79 and secure the indicating unit 78 to base 28. v

The oblong body 77 is provided with an elongated damping chamber 83 having a' substantiallycylindrical wall 84 and a pair of substantially flat Walls 85, 86, :the flat walls diverging from a substantially cylindrical groove87. The bottom 88 ofthe damping chamber 83 is preferably provided with a threaded aperture 89;-adapted'to receive-a bearing screw 90xwhichis'provided with a jewel 91 and secured in place bya set screw The open vupper end 93 of the damping chamber may be closed by a cover plate 94 of a size slightly largerthan the open end 93 and secured in 'placeby screw bolts 95 threaded into'bores'in the insulating flanges 79;

a The cover plate 94 preferably hasan enlarged aperture 96 surrounding, the spindle- 97 -The spindle97 comprises an elongated metal;memberpreferably formed of light metal such .'.as aluminum and provided,v at

' each end with a pivot point 98' comprising a hardened steel point fixedly set in the end of spindle 97. Spindle 97 is also provided with an elongated axially extending slot 99-for receiving the attaching flange 100 of a mag-. netic damping vane 101. The damping vane 101 comprises a substantially rectangular member of magnetic material such as iron which is, substantially complementary in shape to the vertical section of the damping chamber 83, but-is provided with a small clearance 102 with all of the walls of the chamber '83. The, damping vane 101 may be provided with alaterally projecting border flange 103 at its top, bottom and lateral edges for reinforcing the vane'and substantially increasing the damping effect on account iofthe cup action of avane of this type. j l

The attaching flange; 100 ofthe vane 101 is rse'curediin the slot 99 by a plurality of transverse rivets 104 and the axis of the bears ing screw -90 is preferably solocate'd that the damping vane 101l sweeps across the damping chamber 83.with a relatively small leakage of air about the damping vane, but with a certain clearancebetween all parts of the moving element and the supporting body 77. The fiat-wall of the damping chamber 83 is provided with a fixedmagnetic plate 105, preferably of substantially rectangular shape and preferably embedded in the wall 85 and secured by means'of a screw'bolt 106 passing through the wall 85 and threaded into the fixed plate 105. The base 28 is preferably provided with a socket 107 for re ceiving the oblong endeof the body 77 and with asocket- 108 for receiving the bearing screw and nut 92 and-permitting a range of adjustment of the lower bearing.

The indicating unit is preferably provided with a pair of upwardly projecting bridge posts 109, 110 having their reduced threaded ends 111 secured in threaded bores 112 in the insulating body of the indicating unit 78 and the bridge posts 110 are preferablyprovided with reduced threaded upper ends 113 for supporting a bridge 114. The posts 109,110 and bridge 114 are preferably constructed of non-magnetic metal such as brass, and the bridge 114 comprises an elongated strip of metal formed'with a central- 1y located threaded aperture 115 for receiving abearing screw 116, and provided with apertures 117 at each end for receiving the reduced threaded ends 113 of the bridge posts 109,110.

A lock nut 118 secures the bearing screw 116 in any adjusted position and the bearing screw 116 is provided with the usual jewel 119 for pivotally supporting the spindle 97. Cap nuts -120secure the bridge 114 against the shoulders.121 on the bridge'posts and the bridge 114 preferably supports an adjustable spring abutment plate'121 having a spring supporting arm 122. j i

The spindle 97 is provided at its upper end with an annular shoulder'123 against which is secured the pointer 74 and the balance plate 124 which is provided with a plurality of radially projecting balance arms 125, 126, 127. V The spring abutment plate 128 comprises a sheet metal member having an aperture for receiving the reduced upper end 129 of spindle 97 and having an upwardly projecting arm 130 which is fixedly secured to the inner end of a spiral spring 131 of phosphor-bronze or other resilient material. Spring abutment plate 128, balance plate 124 and pointer 74 are all secured against annular shoulder 123 by rivet formations made on the reduced end 129 of the spindle 97. Thev pointer 74 usually formed with an off-set 132and any form of balancing mechanism maybe utilized.

-:I-n the more inexpensive type of instrument, however, the pointer 74may be bal anced by placing drops of solder on the balancearms 125,.126and soldering a'weight asssms 133 to the arm 127 which projects oppositely to the pointer 7 4i.

In order to permit adjustment of the length of the spring 131 to make the amount of the full load deflection correspond to the length of the scale and at the same time cause the pointer to'register at zero or approximatelyv at zero, the spring abutment plate 121 1spreferablyprovided with a centrally loc t? ed aperture 13a for rotatably mounting the abutment plate 121 on the bearing screw 116.

The abutment plate 121 is also preferably formed with a plurality of radial notches 135 in its periphery thereby providing a plurality of teeth 136 between which a latching member 137 carried by zero Corrector plate 26 may be engaged. In some embodiments of the invention the zero corrector plate may be eliminated and the adjustable spring abutment adapted to be latched directlyto the bridge 114:, but in the preferred embodiment the bearing screw 116 also rotatably, supports a zero corrector plate 26 having a cen trally located aperture 138 and a latching member 137. lhe latching member 137 comprises an axially projecting ear or flange on the zero corrector plate 26and adapted to be engaged in the slots 135 formed in theadjustable spring abutment-plate 121.

It should also be understood that the va-'.

retaining the latching device in latched posi- 1 tion such as for instance a spring plate139,

formed with a centrally located enlarged aperture 140 about the bearing screw 116 and provided with apertures 141at each end for receiving the reduced thread-ed ends, 113 of bridge posts 109.

The spring p1ate139is preferably formed with oif-sets 14:2 adjacent eachend and the Y central portion of the spring about the aperture resiliently engages the spring. abutment plate 1.21 and urges the latch 137 into.

latching engagement with the teeth 136.

The latch 137 may be moved out oflatching engagement by spreading the zero correction plate 26 and spring abutment plate'121 against the tension of spring plate139 until the latch 137 passes over the teeth 136. The spring abutment arm 122 is preferably bent downward at 143 through the enlarged aper' ture 1 10 in spring plate 139. The spring abutment plate 121 is slit in'ward at l laon both sides of spring abutment arm 122; so

thatethe: downward bend 1413,1hay .be made 7 close Ztoli' the: bearing. screw 1- 16 inside the spring plateaapert'ure 1:40," and the spring abutment: armis provided with a downwardly turned end 145Ytowhich the spring is secured .by anyi convenient fastening means such. :as-a Ldropv of --solder.- It will. thus be observed? that there" is no interference v.between the: spring. abutment arm 122 and; the spring platel39p or the otherparts of the associated unechanism; and the spring abutment platew121'. is 1. adapted to'be rotated throughout three hundred sixty degrees,.-or DJBTGxWhGH the latch 137 is released.

sks-previously stated, the springt131 is preferably attached} at a point. spaced from its end and tested at full. load current forfull loadascalea deflection', after which the spring maybe .shortened, lengthened,- or the excess length immediatelyclipped off, if thedeflectio'n conforms torstanda-rd. The adjustable spring abutment plate maybe rotated to any desired position after "this adj ustmentof the spring, and. consequently the needle 7 L may be brought back to appr oximatelyi .zero position and the rangeio-fjmovjement of the indi eating unit made {to conform to that of the standard scale.

ment maybe accomplished by the zero correction serew 21, the eccentricpin 24fof which engages'between the' diverging legs 25 of the Zeroicorrectionplate 26. I

"yThe: basicnpirinciplelof. operation=-of the present measuring instrument is fundamen-' tally :tllGj-SZtIIl-B as that of. mostsinstrumentsof the moving jvane type, andineed not, therefore,. .bedescribed in detail. It will thus be observed that I have invented an improved instrument assembly which may be very economically manufactured and which is also capable of giving accurate results for a long period of time withoutnecessity for repair.

The present instrument includes an improved adjustable spring abutment which is provided with positive latching means capable of maintaining the desired adjustment of a spring abutment at all times, but which maybe readily released and adjusted without.

' the necessity for special tools.

While I have illustrated and described a Y specific embodiment ofmy invention. many a The; adjustable spring abutinent plateds adapted i'to be'rotated by the zero correction plate'26 through .the engagementv of the' latch 1371-and'teethi-136 and the i final zero adjust.-

modifications maybe made without depart tails set, forth but desire to avail myself of all changes within the scope of the; appended claims. 1 7

Having thus described myinvention, what I claim as new and desire .to secure by Letters Patent of the United States is:

j 1. zero adjuster for an electrical instruing from thespirit of the invention. and I r donot wish to be limited to the precise de- 6 i p i 7. 1,835,658

ment, comprising a bridge, a bearing screw carried thereby for'supportlng one end of a rotatable element, a spring abutment plate rotatably mounted on said bearing screwand having a radially extending arm for supporting one end of the spring, a zero ad,-

juster plate betweensaid abutment plate and bridge, said abutment plate being formed with a pluralityof radially extending notches and said zero adjusterrplate being formed with an axially extending lug for engaging in said notches, and resilient means for urging said plates together, whereby said plates may be sep arated to remove'said lug from one of said slots and'toeiiect relative rotation between said zero adjustment plate and spring abutment plate. 7 v

2. A Zero adjuster for an electrical instrument, comprising a bridge, a bearing screw carried thereby for supporting one end of a rotatable element, a spring abutment plate rotatably mounted on said bearing screw and having a radially extending arm for supporting one end of the spring, a zero adjuster plate between said abutment plate and bridge, saidabutment plate being formed with a plurality of radially extending notches and said zero adjuster plate being formed with anaxially extending lug for engaging said notches, a pair of bridge posts for supporting said bridge, and resilient means comprising a resilient plate carried by said bridge posts and adapt-ed to urge said plates together, wherebysaid plates may be separated to remove said lug from one of said slots and to effect relative rotation between said zero adjustment plate and spring abutment plate.

In witness whereof, I hereunto subscribe my name this 31 day of July, 1930.

f EDMUND'L. MABIE. 

